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I anyone truing up case heads?

 
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  #1  
Old 07-12-2010, 09:52 AM
tlk tlk is offline
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I anyone truing up case heads?

I noticed that when I am trying to use my honady comparator on some brands of brass I am geting over .001 of variance when I spin the cases in the calipers and the comparator, and all of the chatter is coming from the case head on the caliper jaws.

Did some looking into this and found that the deep stamping on the case head by some mfrs is causing peaks and valleys, and in one case I found the entire head was coned slightly, I suppose becuase the stamping was covering the case head. When I took a couple of the cases that had this issue and ran them across a FINE whetsone (head flat against the stone), this variation went away and was able to get consistent readings. Not a lot of removal - just enough to get rid of the high areas and produce a flat surface to measure off of. Seems to work well, though not techinically "trued".

The reason this is important to me is that if I am using a comparator to set my bullet jump or a slight crush fit/touch to within .001, the friggin' case head may cause me to be off, which throws off the data that I think I am using.

So, is anyone truing up case heads? If so, how are you doing it?

Oh, and, once again, Lapua doesn't seem to suffer from this issue as much as others, and I noticed that their headstamps are much shallower than the rest.

Last edited by tlk; 07-12-2010 at 10:51 AM.
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  #2  
Old 07-12-2010, 11:32 AM
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Re: I anyone truing up case heads?

Just one more problem from mass productionof components. You'r doing the same thing i do on most brass.
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  #3  
Old 07-12-2010, 11:45 AM
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Re: I anyone truing up case heads?

Wilson trimmer system. Turn the case holder around, with the case inserted and go to cranking. Caution: hold the case holder firmly to prevent chatter.

Or, Soup that sucker up and "fire form the head". Repeat the process and the head stamp all but disappears. But not before the case has been rendered useless.
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Old 07-15-2010, 03:21 AM
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Re: I anyone truing up case heads?

[QUOTE=royinidaho;406760]Wilson trimmer system. Turn the case holder around, with the case inserted and go to cranking. Caution: hold the case holder firmly to prevent chatter.


This is an idea alright ....although I shoot lapua brass in 6.5x55 I have not been to technical on the case head truing. I shoot a sporting rifle so I wont figet to much with this as my bullets dont sit so close to the lands anyhow.
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Old 07-16-2010, 07:54 PM
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Re: I anyone truing up case heads?

I drag them across a sheet of extra fine emery paper. It does the same thing you described in your post. It knocks the headstamp burrs down and makes them easier to read too.
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Old 07-17-2010, 06:05 AM
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Re: I anyone truing up case heads?

Quote:
Originally Posted by tlk View Post
I noticed that when I am trying to use my honady comparator on some brands of brass I am geting over .001 of variance when I spin the cases in the calipers and the comparator, and all of the chatter is coming from the case head on the caliper jaws.
How much variation? How are you measuring variation? Over 0.001" isn't particularely specific. If you measure one case over and over spinning it around writing down every measurement how much variation do you see? Of the measurements taken that show variation which one do you think is the most correct of the set?

The reason I ask is that I'm not convinced that 0.001 or even slightly over 0.001" like 0.002" crush variation matters at all for accuracy. Trying for 0.001" extreme spread repeatability on something as flexable and springy as cartridge brass using a gross measurement tool like a digital caliper is like trying to slice cheese with optical precision for a couple of reasons.

Digital calipers aren't good for 0.001" extreme spread in any absolute statistical sense from day to day. Micrometers are but not digital calipers.

The brass can't be counted on to repeat within .001" extreme spread from case to case.

The reason neck sizing can work at all is because the brass has spring back from even as precise a process as the fireforming that happens in a chamber when the round is fired which is the most repeatable thing one ever does with brass. The good news is that springback makes brass usable because with out it extraction of fired cases would be quite difficult. The bad news is that springback makes rifles cases poor candidates for extreme precision when it comes to shoulder set back.

This is further complicated by the fact that nearly all bolt actions (except maybe Savages with their floating bolt head) have 0.001" or more of change in the plane of the bolt face itself between the time the firing pin hits the primer and the bullet leaves the brass because the bolt flops up and down in the rear (which is why bolts are sleeved on some benchrest rifles and some long range rifles).

I could see gently dragging the base across some 800 grit emery to get rid of a burr on some cases just to make measurement easier though I've never done that. Machining the base in a Wilson trimmer might make one feel better but unless it's done very carefully it could result in thinning the rim and increasing the probability of extraction problems.

If it contributes to the fun of reloading and shooting, or eliminates some frustration, with the measurement process, go for it, but I seriously doubt there is any significant difference between brass that's had either process applied and brass not subjected to either process on either the target or game.

Fitch
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Old 07-17-2010, 10:29 AM
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Re: I anyone truing up case heads?

Fitch,

Spot on! Great post.

I don't even mess with it.

Goodgrouper is one that goes ape anal over truing case heads but I never learned how it does it.

The wilson idea I presented was what it was. An idea. Never tried it.
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